1. Two previously unknown amino acids have been identified, and purified from cells of Group N streptococci. The chemical structures and stereochemical configurations of N(5)-(1- carboxymethyl)ornithine and N(6)-(1-carboxymethyl)lysine have been confirmed by chiral syntheses and NMR-spectroscopy. 2. It has been established that the in vivo synthesis of these unusual compounds occurs via the NAD(P)H-dependent reductive condensation between pyruvic acid and the side-chain amino groups of ornithine and lysine. The synthase responsible for the biosynthesis of these novel amino acids has been purified (8000- fold) to homogeneity from cells of Streptococcus lactis K1. The physical and enzymatic properties of the enzyme have been partially defined. 3. The accumulation of sugars (glucose and galactose) by cells of Fusobacterium nucleatum 10953 is dependent upon the provision of glutamic acid, lysine or histidine. These fermentable amino acids provide the energy necessary for sugar transport, phosphorylation and synthesis of endogenous sugar polymer(s). The presence of the amino acids also inhibits the degradation of pre-formed polymer, but in the absence of glutamate, lysine or histidine endogenous polymer is fermented via the Embden-Meyerhof pathway. The concentrations of Na+ and NH4+ ion in the environment markedly affect the rates of sugar transport by resting cells of F. nucleatum. The biochemical roles of